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Name____________________________________
APCS A (Pre-Lab Exercises – 2.3-2.5)
1. What is the difference between a variable and a constant? What reserved word is required to declare
a constant?
2. Explain what each of the lines below does. Be sure to indicate how each is different from the others.
a. int x;
b. int x = 3;
c. x = 3;
3. The following program reads three integers and prints the average. Fill in the blanks so that it will
work correctly.
// *******************************************************************
//
Average.java
//
//
Read three integers from the user and print their average
// *******************************************************************
import java.util.Scanner;
public class Average
{
public static void main(String[] args)
{
int val1, val2, val3;
double average;
Scanner scan = new Scanner(System.in) ;
// get three values from user
System.out.println("Please enter three integers and " +
"I will compute their average");
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//compute the average
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//print the average
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}
}
4. Given the declarations below, find the result of each expression.
int a = 3, b = 10, c = 7;
double w = 12.9, y = 3.2;
a.
a + b * c
_______________
b.
a - b – c
_______________
c.
a / b
_______________
d.
b / a
_______________
e.
a - b / c
_______________
f.
w / y
_______________
g.
y / w
_______________
h.
a + w / b
_______________
i.
a % b / y
_______________
j.
b % a
_______________
k.
w %
y
_______________
5. Carefully study the following program and find and correct all of the syntax errors.
// File:
// Purpose:
//
Errors.java
A program with lots of syntax errors
Correct all of the errors (STUDY the program carefully!!)
#import java.util.Scanner;
public class errors
{
public static void main (String[] args)
{
String Name; / Name of the user
int number;
int numSq;
Scanner scan = new Scanner(System.in);
System.out.print ("Enter your name, please: ")
Name = scan.nextInt();
System.out.print ("What is your favorite number?);
number = scan.nextInt();
numSq = number * number;
System.out.println (Name ", the square of your number is "
numSquared);
}
6. Trace the execution of the following program assuming the input stream contains the numbers 10, 3,
and 14.3. Use a table that shows the value of each variable at each step. Also show the output (exactly
as it would be printed).
// FILE: Trace.java
// PURPOSE: An exercise in tracing a program and understanding
//
assignment statements and expressions.
import java.util.Scanner;
public class Trace
{
public static void main (String[] args)
{
int one, two, three;
double what;
Scanner scan = new Scanner(System.in);
System.out.print ("Enter two integers: ");
one = scan.nextInt();
two = scan.nextInt();
System.out.print("Enter a floating point number: ");
what = scan.nextDouble();
three = 4 * one + 5 * two;
two = 2 * one;
System.out.println ("one " + two + ":" + three);
one = 46 / 5 * 2 + 19 % 4;
three = one + two;
what = (what + 2.5) / 2;
System.out.println (what + " is what!");
}
}